As a locking mechanism when a seat back is stopped at a predetermined angle of inclination, Patent Document Nos. 1 and 2 disclose a technique that uses a sliding member that abuts on a worm tooth surface to stop rotation of a worm through friction, and a technique that moves the worm in a parallel manner toward a worm wheel to press the worm against the worm wheel to stop rotation of the worm through friction. Also, Patent Document No. 3 discloses a technique that forms a tapered surface on a circumference of an axis portion at one end of an axially supported worm and moves a brake member that can contact the tapered surface to stop rotation of the worm through the friction between both members.
However, the techniques disclosed in Patent Document Nos. 1 to 3 stop rotation of the worm through friction by pressing the sliding member or brake member without changing the posture of the worm, in other words while maintaining the posture of the worm axially supported at a predetermined position. Both Patent Document Nos. 1 and 2 describe also moving the worm toward the worm wheel. However, since the movement of the worm is ultimately parallel, the worm engages the worm wheel while maintaining the posture of the worm supported at a predetermined position.
Backlash exists between each of the teeth of the worm and that of the worm wheel to allow for smooth rotational movement, but this backlash is a cause of rattling or abnormal sound when the seat back is locked. The techniques disclosed in Patent Document Nos. 1 to 3 specifically relate to locking techniques to securely stop the worm, so no attention is paid to preventing the generation of rattling or abnormal sound when locking. However, these techniques press the worm against the worm wheel while maintaining the posture of the worm and substantially provide a deceleration function of the backlash when locking.
However, this backlash is not always constant due to manufacturing errors of the teeth on the worm and the worm wheel. This also varies depending on friction and deformation of the teeth through use. For that reason, the gaps between mutually meshing teeth can be larger than the appropriate clearance that can be defined as a smooth operation for backlash. In such a case, even when the worm is pressed to the worm wheel, a large clearance is generated between each of the teeth of the worm and that of the worm wheel, and the clearance can be the cause of rattling and abnormal sound when locking.
On the other hand, Patent Document No. 4 discloses a mechanism in which one end of the worm is supported by a movable bearing, and an end of the movable bearing is pressed using a compression spring. Since the movable bearing is moved by the compression spring, the worm is pushed to the gear side that is meshed therewith, and the backlash between the worm and the gear is reduced. However, the elastic force of the compression spring (force to push the worm to the gear side) is configured not only to act when stopping the rotation of the worm, but also while the worm is rotating. During the rotation, it is necessary to ensure an appropriate backlash between the teeth of the both, but in the case of Patent Document No. 4, the worm is continuously pressed by the compression spring also while the worm is rotating. Therefore, it is not possible to ensure the backlash that is required during the rotating operation, and the movement of the worm is not smooth.
In view of the points outlined above, the applicants propose, as described below to Patent Document No. 5, a mechanism that not only has a locking mechanism of the worm, but also eliminates clearance in the thrust direction of the worm when locking. The mechanism, however, does not interrupt smooth rotation of the worm when the seat back is being reclined.
In other words, Patent Document No. 5 proposes a reclining adjuster that uses a worm respectively formed with recesses at both ends, respectively secures to the brackets bearings having cavities at surfaces opposing the worm and adopts a support mechanism for the worm provided with a ball between each of the worm and the bearing to lock the teeth of the other end of the axial direction of the worm using pressing means when the seat back is stopped at a predetermined angle of inclination.
Through this, when the seat back is locked, the worm at the other end side in the axial direction is rotated about an end side thereof in the axial direction slightly toward the worm wheel side, and the ball of the other end in the axial direction moves slightly along the inner surface of the recess. Thus, an axial center of the worm is pushed to the worm wheel in a slightly oblique state. The result is that force acts on the worm in one end direction of the axial direction to the other end side of the axial direction by the ball, and the worm is slightly displaced in the thrust direction. For that reason, backlash is eliminated, and it is possible to eliminate clearance in the thrust direction of the worm even when there is much clearance. Therefore, it is possible to inhibit rattling and abnormal sounds of the seat back caused by the clearance. On the other hand, since when the seat back is being reclined, the worm is not pressed by the worm wheel, an appropriate amount of backlash required in the operation is ensured and the rotation of the worm is not hindered.
Patent Document 1: Publication of German Unexamined Patent Publication No. DE4422529A1
Patent Document 2: U.S. Pat. No. 5,590,562
Patent Document 3: Unexamined Patent Publication No. 08-38289
Patent Document 4: Utility Model Application No. 56-126667 (Unexamined Utility Model Publication No. 58-35175) Specifications and Drawings
Patent Document 5: Unexamined Patent Publication No. 2003-319849